The present invention relates to a single wire dryer group having a plurality of heatable drying cylinders and having at least one respective reversing roll disposed between two adjacent drying cylinders. The invention particularly relates to the adjustability of the reversing rolls. A support belt for the web to be dried, particularly an endless support belt or dryer wire, travels along a pathway which passes over a drying cylinder, then over a reversing roll and then over the next drying cylinder, and so on through the dryer group.
Published International specification WO 83/00514 discloses a single wire dryer group in which the distances between the drying cylinders and the neighboring reversing rolls, which are preferably suction guide rolls, can be very small in order to reduce as much as possible the elongation or tensile stressing of the web of paper, and thus to also reduce the crosswise contraction of the web upon departure of the web from each of the drying cylinders. That reference discloses supporting the reversing rolls in movable bearings so that the introduction of a new drying wire by means of transverse bars is possible. Another advantage is that there is no danger to the rolls or bearings if the web of paper should wrap up on one of the drying cylinders in the event that the web of paper tears.
In accordance with FIG. 2 of the above reference, the reversing rolls are so mounted on a swing lever that, when the drying cylinders are arranged in a horizontal row, the reversing rolls can be moved in the vertical direction away from the drying cylinders or back into their original positions.
A similar construction is disclosed in U.S. Pat. No. 4,905,379. One disadvantage of this construction is that upon each displacement of a reversing roll, the wire tensioning roll must be moved over a relatively large distance. This movement of the wire tensioning roll can generally take place only at slow speed. Thus, the process of displacing the reversing roll also always takes place very slowly. There is the additional disturbing factor that, at times, several reversing rolls of the same dryer group must be displaced simultaneously. Accordingly, the wire tensioning roll must then be moved over an even larger distance.
A drying end or dryer group with rigidly mounted reversing rolls is also known from Federal Republic of Germany Utility Model 9001210, corresponding to U.S. application 467,788, filed Jan. 19, 1990, in which the distance between the periphery of a reversing roll and the periphery of the preceding web delivering drying cylinder is less than the distance between the periphery of that reversing roll and the periphery of the following web receiving drying cylinder. The reversing roll is therefore arranged asymmetrically with respect to the two adjacent drying cylinders. On the one hand, the web of paper remains adhering relatively reliably on the support belt or drying wire at the point of its departure from the web delivering cylinder. This results, as already mentioned, in reduction in the longitudinal stretching of the web. On the other hand, an enlarged zone is obtained between the reversing roll and the web receiving cylinder. Within that zone, water vapor can emerge from the web of paper. An air blast box can also be arranged in that zone. This proposal has the disadvantage that the distance between the reversing roll and the preceding web delivering cylinder can still not be made sufficiently small since the reversing rolls are installed in fixed positions. That distance amounts to between 30 mm and 100 mm.